1. Field of the Invention
The invention relates to a device for continuous casting of metal, in particular steel, and including a metal mold with mold walls and a mold cooling device. Such a device serves for casting strands of different sizes, e.g., slabs, thin slabs, blooms, or beam blanks (dog bones). Here, the mold itself or the strand can oscillate, as during horizontal continuous casting. The mold itself, however, is arranged at a predetermined location and, therefore, can be called a continuous casting mold.
2. Description of the Prior Art
Such a mold, as a casting mold for continuous casting plants, consists either of mold plates, namely, of two plates for the mold broad sides and two plates for the mold narrow sides, or of mold tubes.
Such mold plates or mold tubes are formed of copper and have, as a rule, a thickness from 10 to 50 mm between the water cooling side and a side adjacent to the steel melt.
The selection of the copper plate thickness depends on the thermal load or the thermal flow measured in MWh/m2 or MW/m2. Thus, continuous casting plants with a mold for slab sizes with a thickness greater than 150 mm and width 3 m, with a casting speed of maximum about 2.5 m/min, have a thermal flow of maximum 2 MW/m2. The thickness of the copper plates of the mold lies between 25 and 50 mm. In comparison, the thin slabs, which are cast with a casting speed up to 10 and in the future up to 15 m/min, have a thermal flow of maximum 4-5 MW/m2 and copper plate thicknesses from 10 to 25 mm.
In order to match the increased thermal flow with the increased casting speed, the copper wall must always be thinner with the intensification of water cooling. This is difficult because a thinner mold wall always withstands worse high water pressures of 5-15 bar, which are necessary for a corresponding water velocity of 5-15 m/sec, without being deformed. An additional drawback consists in that the thin copper plates lose their rigidity when the recrystallization temperature exceeds its threshold at a too high thermal load of the cold-rolled copper. Besides, there is a problem of mounting of very thin copper plates on the mold frame. Usually, the mold plates are secured on a water box or a mold frame with bolts which are secured into the plates with their threaded section. This is not possible with very thin plates; in this case, the bolts must be welded to the copper plates.
An object of the invention is to so improve the devices of the above-described type so that the above-mentioned drawbacks are eliminated despite the increase of the casting speeds. In particular, a device for continuous casting with a mold should be provided which is capable of leading away of high thermal flows and can, therefore, be subjected to high thermal loads. Also the assembly should be improved.
This object is achieved by a device with the features of claim 1. Advantageous further developments are described in the sub-claims.
According to the invention, it is proposed that at least one mold wall includes a steel wall and a support mesh for the steel wall, that a magnetic field generator for generating a magnetic field is provided, which acts on the steel wall via the support mesh, and that the mold cooling device includes a spray cooling device.
The foregoing features permit to provide a mold having a thin mold wall with a high and controllable heat dissipation characteristics even at high casting speeds. The mold wall is formed, on one hand, of a steel wall facing the metal melt and, on the other hand, of a support mesh for stabilizing the steel wall. Because of magnetic attraction forces, the steel mold wall can be easily mounted. In addition, such a mold has a particular advantage consisting in that the steel mold wall, which is wearable because of its exposure to the metal melt, if needed, can be, contrary to an expensive copper wall, rapidly and simply replaced without a high-quality treatment, while the used one is xe2x80x9cthrown awayxe2x80x9d, i.e., is subject to a steel-recycling process. With the contemplated double wall, which consists of a thin steel wall and a support mesh, a simple and relatively inexpensive mold spray cooling can be used. In order to avoid high mold cooling water pressures, e.g., of 15-20 bar, the spray cooling takes place in open chambers or passages left by the support mesh, i.e., the thin steel wall is directly cooled, while being provided, despite this, with a relatively high support. With the spray cooling, the use of splash water becomes possible. Overall, along with a high efficiency of heat dissipation, a simple mold construction and, therefore, a relatively inexpensive mold is obtained. The inventive solution provides a mold that has a thermal conduction which otherwise would have required a copper plate thickness of 10 mm or more, and that can be easily mounted on a base frame, while permitting water cooling and being, at the same time, very economical.
The steel mold wall according to the present invention has preferably a thickness between 0.5 and 5 mm and corresponds, in its effectiveness, to a copper plate having a thickness of 10 mm, while having a definite constructional and economical advantage.
Preferably, the support mesh has a support wall with chambers formed therein, so that separate chambers or passages of the mesh are surrounded by wall webs of the support wall, with the magnetic field being introduced in the mold wall via the support wall.
The spray-cooling for cooling the mold wall includes, preferably, spray nozzles extending in the chambers of the support mesh at a side of the support mesh remote from the steel wall, i.e., through the freely accessible chamber regions or openings in the mesh. These spray nozzles for mold spray-cooling and the conduits for the cooling medium, in particular water, are integrated, completely or partially, in the support walls of the support mesh.
The advantage of the proposed spray cooling consists in that the intensity of the spray cooling is functionally adjusted in accordance with energy flow in the mold wall over the mold height. The energy flow has a thermal maximum somewhat in the upper third of the mold. With the spray cooling with separate, arranged one above the other, nozzles, the intensity of cooling can be adjusted in a controlled manner and, thereby, to be adapted to an energy flow with energy maximum or to an energy unit, as it is in this point a more intensive cooling takes place.
According to a further development of the device, it is contemplated to provide a device for controlling the surface temperature of the side of the steel mold wall adjacent to the liquid metal in order, when necessary, to adapt the spray cooling, by using a regulating mechanism, to fluctuation of the surface temperatures.
In addition to the proposed, according to the invention, attachment of the steel mold plate to the support mesh, the mold plate can be additionally secured mechanically. To this end, it is proposed to use a fixation device for securing the steel mold wall, e.g., a broad side in the middle of the broad side with respect to the mold height. In addition, the steel mold wall can be horizontally secured at the mold inlet or mold outlet. In addition to the broad sides, if necessary, the narrow sides can be secured in case they are likewise stabilized by a support mesh.
According to a particularly advantageous embodiment, the support walls of the support mesh are provided, at their ends facing the steel mold wall, i.e., in their fore-side or their head with a ball that serves as a (ball) bearing for a free, heat-dependent, movement of the steel mold plate. In order to form a fluid bearing, the balls are filled with fluid medium, e.g., water or gas. To this end, conduits are formed in the support walls which extend transverse to the steel mold wall and which supply the balls or the ball cages with water at the end sides of the support walls.
In order to prevent an uncontrolled flow of the spray water away after it has been sprayed on the free rear wall regions of the steel mold wall, according to the further development of the present invention, the support mesh includes an outer frame with a sealing surrounding the mesh.
Backward, i.e., toward the side remote from the steel melt, the used cooling medium can either flow freely away, i.e., flow to the atmosphere, or flow directly along. In the second case, preferably, a collection chamber is provided at the lower portion of the mold wall which opens into a drain for bringing the cooling water, if necessary, to a processing plant. In the collection chamber, the cooling medium, which flows along the support mesh wall, in particular along a wall portion of the support mesh located below a respective spray nozzle, is collected and is evacuated through the drain.
Further features and advantages of the invention follow from the sub-claims and from the following description that explains in detail embodiments of the invention shown in the drawings which include the above-described combination of features, separate features alone, or other essential combinations. The drawings show: